The urinary tract has a pair of kidneys that connect to a bladder by ureteral passageways, and a urethra that extends from the bladder to the exterior of a patient. Urine is made by the kidneys, passed through the ureteral passageway, stored in the bladder and ultimately voided from the urethra. A urinary sphincter is positioned around the urethra near the base of the bladder to control the flow of urine from the bladder.
The ureteral passageways normally allow urine to pass from the kidney to the bladder by peristalsis. When the bladder fills with urine, the bladder compresses a segment of the ureteral passageway that passes through a wall of the bladder to prevent urine from going backwards from the bladder into the kidney. These passageways can become blocked by tumors or kidney stones thereby preventing normal urine flow, and the resulting high pressure within the kidneys can cause pain to the patient. To reopen a blocked ureteral passageway, a ureteral stent can be positioned in the patient. The stent holds the blockage in the passageway open, for example to allow a small kidney stone to pass. This enables urine to flow from the kidney into the bladder, reduces kidney pressure, and reduces pain of the patient.